It is known that synthetic resins can be used as binders for inorganic-oxidic materials such as sand in the production of foundry articles. Cold-curing resin systems based on phenolic resins, furan resins or 2-component polyurethane resins, for instance, are of great importance. A resin system which was introduced some years ago is an alkali/phenol/formaldehyde binder which is cured by an ester as a gassing agent or as a liquid. These foundry resin systems are described, for instance, in published European Applications Nos. 85512 and 86615. Such a resin system is called an ester-curing resin.
It is also known that selected organofunctional silanes improve the adhesion of resins to inorganic-oxidic materials (see German Offenlegungsschrift No. 28 29 669). The aforementioned published European patent applications disclose that aminoalkyltrialkoxysilanes, such as 3-aminopropyltriethoxysilane, improve the adhesion when added to ester-curing resins.
However, for many applications the adhesion between the resin binder and the inorganic-oxidic material was only slight, and consequently the strength of the shaped articles produced therefrom, such as cores or shells of foundry molds, was unsatisfactory. In connection with the solution of this problem consideration had to be given to the fact that the ester-curing resins are aqueous, highly alkaline systems having a pH of more than 12. With the exception of aminofunctional silanes, organofunctional silanes are not stable in an aqueous alkaline medium and condense very rapidly after hydrolysis to form polysiloxanes (Noll, Chemie Und Technologie der silicone, Verlag Chemie, Weinheim, Germany, 1968; and Plueddemann, Silane Coupling Agents, Plenum, N.Y., 1982).